Component is not displaying on panel

Question

My own component is not is not displaying on panel.

import rysujdrzewo.nodeLabel.NodeLabel;
import rysujdrzewo.nodeLabel.PointOfContact;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import javax.swing.JComponent;

public class PaintLinesBetweenNodes extends JComponent{
    private final NodeLabel oNode1;
    private final NodeLabel oNode2;
    private final PointOfContact oPointForNode1;
    private final PointOfContact oPointForNode2;
    private final String sEdgeName;

    public PaintLinesBetweenNodes(NodeLabel oNode1,NodeLabel oNode2, PointOfContact oPointForNode1, PointOfContact oPointForNode2, String sEdgeName){
        super();
        this.oNode1 = oNode1;
        this.oNode2 = oNode2;
        this.oPointForNode1 = oPointForNode1;
        this.oPointForNode2 = oPointForNode2;
        this.sEdgeName = sEdgeName;
    }

    private void paintNodeConnections(Graphics2D oGraphics) {
        Point p1 = oNode1.getConnectionPoint(oPointForNode1);
        Point p2 = oNode2.getConnectionPoint(oPointForNode2);

        oGraphics.drawLine(p1.x, p1.y, p2.x, p2.y);
        oGraphics.drawString(sEdgeName, (float)(p1.x + p2.x) / (float)2,  (float)(p1.y + p2.y) / (float)2);
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        paintNodeConnections(g2d);
    }
}

This one is displaying correctly:

import java.awt.Point;
import java.awt.event.ComponentEvent;
import java.util.HashMap;
import java.util.Map;
import javax.swing.JLabel;

public class NodeLabel extends JLabel{
    Map<PointOfContact, Point> connectionPoints = new HashMap<>();

        public NodeLabel(String text) {
            super(text);
            addComponentListener(new java.awt.event.ComponentAdapter(){
                 @Override
                 public void componentResized(java.awt.event.ComponentEvent evt) {
                    mapConnectionPoints();
                }
                 @Override
                public void componentMoved(ComponentEvent e) {
                    mapConnectionPoints();
                }

            });
        }

        // updates the mapped positions of the connection points
        // called whenever the component get's resized or moved
        private void mapConnectionPoints(){
            connectionPoints.clear();
            Point point = new Point(getX(),getY()+getHeight()/2);
            connectionPoints.put(PointOfContact.LEFT, point);

            point = new Point(getX() + getWidth(), getY() + getHeight()/2);
            connectionPoints.put(PointOfContact.RIGHT, point);

            point = new Point(getX() + getWidth()/2, getY());
            connectionPoints.put(PointOfContact.TOP, point);

            point = new Point(getX() + getWidth()/2, getY() + getHeight());
            connectionPoints.put(PointOfContact.BOTTOM, point);
        }

        public Point getConnectionPoint(PointOfContact key) {
            return connectionPoints.get(key);
        }
}

and execution:

import java.awt.Color;
import java.awt.Dimension;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import static javax.swing.JFrame.EXIT_ON_CLOSE;
import javax.swing.JPanel;
import javax.swing.SwingConstants;
import rysujdrzewo.nodeLabel.NodeLabel;
import rysujdrzewo.nodeLabel.PointOfContact;


public class PaintTree extends JFrame{

    public PaintTree() {
        initComponents();
    }

    private void initComponents() {
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setMinimumSize(new Dimension(800, 800));
        JPanel oJPanel = new JPanel();
        oJPanel.setLayout(null);

        NodeLabel oNode1 = new NodeLabel("Node 1");

        oNode1.setHorizontalAlignment(SwingConstants.CENTER);
        oNode1.setBorder(BorderFactory.createLineBorder(new Color(0, 0, 0)));
        NodeLabel oNode2 = new NodeLabel("Node 2");

        oNode2.setHorizontalAlignment(SwingConstants.CENTER);
        oNode2.setBorder(BorderFactory.createLineBorder(new Color(0, 0, 0)));

        NodeLabel oNode3 = new NodeLabel("Node 3");

        oNode3.setHorizontalAlignment(SwingConstants.CENTER);
        oNode3.setBorder(BorderFactory.createLineBorder(new Color(0, 0, 0)));

        oJPanel.add(oNode1);
        oJPanel.add(oNode2);
        oJPanel.add(oNode3);
        PaintLinesBetweenNodes o1 = new PaintLinesBetweenNodes(oNode1, oNode2, PointOfContact.BOTTOM, PointOfContact.TOP, "Czesc1");
        PaintLinesBetweenNodes o2 = new PaintLinesBetweenNodes(oNode1, oNode3, PointOfContact.BOTTOM, PointOfContact.TOP, "Czesc2"); 

        oJPanel.add(o1);
        oJPanel.add(o2);

        getContentPane().add(oJPanel);
        oNode1.setBounds(100, 52, 56, 28);
        oNode2.setBounds(54, 200, 56, 28);
        oNode3.setBounds(150, 200, 56, 28);

        pack();
    }
}

I have no idea what's wrong with this code. I don't use any layouts because I try create some graphical representation of tree data(Decision tree).

Answer 1

Basically, you never set the size of your instances of PaintLinesBetweenNodes, meaning that they will have an initial size of 0x0

This is one of the problems of using a null layout, you become responsible for sizing an positioning of the components

I also think you'll find pack won't work they way you expect it to, as it relies on the information supplied by the layout managers